In a conventional switching power supply apparatus described in Japanese Patent Application Publication No. Hei 7-115774, two rectifying elements of a bridge-type full-wave rectifying circuit situated on a side where a feedback current flows are replaced with switching elements 104a and 104b, respectively, as shown in FIG. 1. This switching power supply apparatus is called bridgeless PFC, and its power factor, conversion efficiency, and reliability are improved by allowing a control circuit 106 to control the switching elements 104a and 104b appropriately.
Moreover, as shown in FIG. 2, the switching power supply apparatus distinguishes the upper half (positive voltage) and the lower half (negative voltage) of the wave of an AC input voltage, and causes the switching elements 104a and 104b to operate in synchronization with the upper and lower halves of the wave, respectively. In this case, in each of the switching elements 104a and 104b, a switching mode period and an ON-state fixing mode (synchronous rectification mode) period are switched in accordance with the polarities of the AC input voltage.
By the above configuration, the switching power supply apparatus described in Japanese Patent Application Publication No. Hei 7-115774 can improve its power factor, efficiency, and reliability.
However, in the conventional switching power supply apparatus, the operations of the switching elements 104a and 104b are unstable, making it impossible to achieve a sufficient improvement in power factor in particular.